Currently, radio frequency or mixed signal system in portable/wearable electronics is urgently calling for heterogeneous integration (for example, integration of radio frequency, digital, and power systems) and reduced form factor so as to meet the need in miniaturizing the size of products. Advanced packaging technology such as three-dimensional packaging is a potential solution to achieve this.
Considering signal integrity, radio frequency and digital/power signal paths should be electrically separated, and low loss substrate such as low temperature co-fired ceramic is recommended to route high frequency or ultra high frequency signals.
On the other hand, another critical issue is that radio frequency integrated circuit, being a sensitive device, should be electromagnetically shielded, while its antenna still keeps unaffected.
U.S. Pat. No. 6,657,523 discloses a stacked radio-frequency module formed by stacking packages each storing monolithic microwave integrated circuits (MMICs) and mounting another package upside down which stores a control circuit for controlling MMICs. The MMICs and control circuits are each sealed by a metal sealing lid within the cavity of each of the packages which are spatially completely separated from each other. Each of the pads for wiring paths for radio-frequency signals and for power supply/control signals and ground pads are provided within each package and at opposing surfaces of packages to be stacked with corresponding pads joined by a gold bump.
U.S. Pat. No. 7,477,197 provides an integration of antenna and RF front-end module, relating an electronic assembly including a substrate having a first surface and a second surface opposite the first surface. The electronic assembly also includes a RF front-end module coupled to the first surface of the substrate, and a ground plane layer positioned on the second surface of the substrate, an insulating layer on the ground plane layer, with the ground plane layer positioned between the second surface and the insulating layer. In addition, the electronic assembly further comprises an antenna layer on the insulating layer, with the insulating layer positioned between the antenna layer and the ground plane layer.
U.S. Pat. No. 8,335,084 discloses an electronic system or module which includes embedded actives and discrete passives, and methods for use in fabricating packages containing embedded active devices and/or discrete passive devices. The module comprises a plurality of build-up layers defining circuit interconnections and that comprise one or more thin film type of embedded passive devices, at least a cavity formed in the build-up layers, and at least an active device and/or at least a discrete passive device disposed in the cavity and electrically connected to the circuit interconnections of the build-up layers. The build-up layers may be mounted to a core, and the core may be attached to a printed circuit board.
Nonetheless, the above prior arts fail to provide a packaging system for radio frequency signals, which carries optimized performance in electrical properties and EM shielding, an ultra-small form factor, and a low cost solution at the same time.